1. Field of the Invention
This invention relates to a device for filtering liquids. In particular, this invention relates to replaceable filters for use in water treatment systems.
2. Description of the Related Art
Unwanted and potentially harmful contamination in water, especially drinking water, is of concern to many people. This concern creates a desire for water treatment devices in the home and elsewhere. Many water treatment devices and methods have been developed to remove or neutralize particulate and chemical contaminants.
Water treatment devices are well known in the art. These devices can be employed directly in a water system, either in-line or at a terminal end, or also in self-contained batch systems. An example of an in-line system is an under-the-counter device that filters water in the source line before it reaches the faucet. Terminal end devices include countertop and faucet-mounted filtration systems. These systems rely on pressure in the water system to drive water through the filtration device. Self-contained batch systems typically have upper and lower chambers separated by a filter cartridge, all within a pitcher or carafe. They rely on gravity to move water from the upper chamber, through the cartridge, and into the lower chamber, thereby producing treated water.
Typically, water treatment devices employ mechanical filtration and/or chemical treatment. Mechanical filters treat water by preventing passage of particulates. Chemical treatment) employs processes such as adsorption and ion exchange for removing undesirable chemical species. Many common chemical treatment devices use activated carbon-based and ion exchange media either in block form or as loose media in a container.
Some consumers are reluctant to change a water treatment device unless they have some indication that the device is “used up”. As a mechanical filter approches the end of its useful life, restricted flow due to particulate accumulation can provide a ready indication that filter replacement is necessary. A major drawback associated with chemical treatment is that the chemical treatment medium eventually becomes inactive, yet provides no direct indication that its useful life is over.
Consumers are more satisfied with a product when they have direct evidence that the product is functioning. Although chemical treatment provides additional water purification not possible with mechanical filtration alone, it is difficult for consumers to have an indication that these systems are working actively except, of course, by the subjective taste of the treated water.
Some methods have been employed to provide a visual indication of particulate filtration on pressure-driven water treatment systems. One method is disclosed by Lang in U.S. Pat. No. 4,686,037, wherein a user can compare the color of a pre-filter on a faucet-mounted water filter with a reference strip as an indication of particulate collection.
Indication of chemical species removal has been more elusive. For example, activated carbon can remove undesirable tastes and odors from water as well as chlorine and other reactive chemicals. Ion exchange resins are useful for removing metal and other ions. Many consumers are not aware of the specific chemical contaminants in their tap water. Although current water treatment devices may be successful in removing these contaminants, a consumer has no direct indication of what has been removed. An indicator of specific chemical contaminants in the untreated water, which contamination can be removed by the treatment device, would aid greatly in increasing customer satisfaction with water treatment systems.
Accordingly, there is a need for improved materials for filter components that allow gravity-fed water treatment devices to give consumers a particle contaminant indicator that was heretofore possible only on pressure-driven water treatment systems. There is a further need to increase consumer satisfaction with water treatment systems by providing an indication of specific chemical contaminant removal.